CN110213459B - Display method and display device - Google Patents

Detailed Description

(knowledge as a basis of the present invention)

The present inventors have found that the following problems occur with the image signal processing apparatus described in the "background art" section.

On the basis of the above studies, the present inventors have studied the following improvement countermeasures in order to solve the above problems.

A conversion method according to an aspect of the present invention converts luminance of a video displayed on a display device, the luminance of the video being composed of luminance values in a 1 st luminance range, acquires a 1 st luminance signal indicating a code value obtained by quantizing the luminance values of the video, and converts the code value indicated by the acquired 1 st luminance signal into a 2 nd luminance value corresponding to a 2 nd luminance range, the 2 nd luminance range being a range determined according to the luminance range of the display device, and a maximum value of the 2 nd luminance range being smaller than a maximum value of the 1 st luminance range and larger than 100 nit.

According to this aspect, the luminance can be appropriately converted from the 1 st luminance range to the 2 nd luminance range in which the luminance range is reduced.

For example, the following 1 st luminance conversion may be performed in the conversion to the 2 nd luminance value: determining a 1 st luminance value associated with the 1 st code value in the EOTF for the 1 st code value represented by the obtained 1 st luminance signal, using an Electro-Optical Transfer Function (EOTF) that associates a luminance value in the 1 st luminance range with a plurality of 1 st code values, determining a 2 nd luminance value corresponding to the 2 nd luminance range, which is previously associated with the 1 st luminance value, for the determined 1 st luminance value, and converting the 1 st luminance value corresponding to the 1 st luminance range into the 2 nd luminance value corresponding to the 2 nd luminance range.

For example, the maximum value of the 2 nd luminance range may be the maximum value of the luminance of the display device, and the 1 st luminance conversion may determine the 2 nd maximum luminance value, which is the maximum value of the luminance of the display device, as the 2 nd luminance value when the 1 st luminance value is the 1 st maximum luminance value, which is the maximum value of the luminance values of the plurality of images constituting the video.

For example, in the 1 st luminance conversion, when the 1 st luminance value is equal to or less than an average luminance value that is an average of luminance values of a plurality of images constituting the video, the 1 st luminance value may be determined as the 2 nd luminance value without converting the 1 st luminance value, and when the 1 st luminance value is equal to or more than the 1 st maximum luminance value, the 2 nd maximum luminance value may be determined as the 2 nd luminance value.

For example, in the 1 st luminance transformation, when the 1 st luminance value is between the average luminance value and the 1 st maximum luminance value, the 2 nd luminance value corresponding to the 1 st luminance value may be determined using a natural logarithm.

For example, luminance information including at least one of the 1 st maximum luminance value and an average luminance value that is an average of luminance values of a plurality of images constituting the video may be acquired as meta information of the video.

For example, the 1 st luminance signal may be acquired from a recording medium, and luminance information including at least one of the 1 st maximum luminance value and an average luminance value that is an average of luminance values of a plurality of images constituting the video may be acquired via a network.

For example, luminance information corresponding to each of a plurality of scenes of the video image may be acquired, that is, luminance information including at least one of the 1 st maximum luminance value, which is a maximum value among luminance values of a plurality of images constituting the scene, and an average luminance value, which is an average of luminance values of the plurality of images constituting the scene, may be acquired for each of the scenes, and the 2 nd luminance value may be determined based on the luminance information corresponding to each of the scenes in the 1 st luminance conversion.

For example, a 2 nd luminance conversion may be performed, in which a 3 rd luminance value corresponding to a 3 rd luminance range having a maximum value of 100nit, which is previously associated with the 2 nd luminance value, is determined for the determined 2 nd luminance value, the 2 nd luminance value corresponding to the 2 nd luminance range is converted into the 3 rd luminance value corresponding to the 3 rd luminance range, the 3 rd luminance value is quantized using an inverse EOTF in which a luminance value in the 3 rd luminance range and a plurality of 3 rd code values are associated with each other for the determined 3 rd luminance value, a 3 rd code value obtained by quantization is determined, the 3 rd luminance value corresponding to the 3 rd luminance range is converted into a 3 rd luminance signal representing the 3 rd code value, and the 3 rd luminance signal is output to the display device.

For example, in the 2 nd luminance conversion, luminance-related information corresponding to display characteristic information that is information indicating display characteristics of the display device may be used for the determined 2 nd luminance value, the luminance value related to the 2 nd luminance value may be determined as the 3 rd luminance value, and the luminance conversion process may be switched according to the display characteristic information.

For example, the display characteristic information may be a display mode of the display device, and in the 2 nd luminance conversion, when the display mode is a normal mode, the 3 rd luminance value luminance may be converted into a proportional value proportional to the 2 nd luminance value, and when the display mode is a dynamic mode in which a high-luminance pixel is brighter than the normal mode and a low-luminance pixel is darker than the normal mode, the 3 rd luminance value luminance of the low-luminance pixel may be converted into a value higher than a proportional value proportional to the 2 nd luminance value, and the 3 rd luminance value luminance of the high-luminance pixel may be converted into a value lower than a proportional value proportional to the 2 nd luminance value.

For example, in the 1 st luminance conversion, the 2 nd maximum luminance value may be determined using display characteristic information that is information indicating display characteristics of the display device.

For example, the display characteristic information may be acquired from the display device.

For example, the display characteristic information may be acquired immediately before the conversion to the 2 nd luminance value.

For example, the display characteristic information may be acquired at the time when the connection to the display device is started.

These general and specific aspects may be realized by a device, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or any combination of the device, the integrated circuit, the computer program, and the recording medium.

A display method and a display device according to an embodiment of the present invention will be described in detail below with reference to the drawings.

The embodiments described below are intended to illustrate a specific example of the present invention. The numerical values, shapes, materials, arrangement positions and connection modes of constituent elements, steps, order of steps, and the like shown in the following embodiments are merely examples, and the gist thereof is not limited to the invention. Among the components of the following embodiments, those not recited in the independent claims indicating the highest concept will be described as arbitrary components.

(embodiment mode)

The present invention relates to an image conversion/reproduction method and apparatus for displaying an HDR (High Dynamic Range) signal, which is a High luminance signal having a High luminance Range, on a display device such as a TV, a projector, a tablet, or a smartphone, which corresponds to an SDR (Standard Dynamic Range) signal, which is a normal luminance signal having a luminance Range with a maximum luminance value of 100 nit.

[1-1. background ]

First, transition of the imaging technique will be described with reference to fig. 1. Fig. 1 is a diagram for explaining the development of the imaging technology.

Heretofore, as for the improvement of image quality of a video, mainly focusing on the expansion of the number of display pixels, a video having 720 × 480 pixels in Standard Definition (SD) to a so-called 2K video having 1920 × 1080 pixels in High Definition (HD) has been widely used.

In recent years, for the purpose of further improving the image quality, a so-called 4K video of 3840 pixels × 1920 pixels or 4096 pixels × 1920 pixels of 4K has been introduced, which is Ultra High Definition (UHD).

Further, it is also studied to improve the image quality by increasing the resolution of an image by introducing 4K, and by expanding the dynamic range, expanding the color gamut, adding or improving the frame rate, and the like.

Among them, the Dynamic Range is receiving attention as a method for expanding a luminance Range of a maximum luminance value so as to express bright light such as specular reflection light which cannot be expressed in a current TV signal with brightness closer to reality while maintaining a dark portion gradation in a conventional video, and as a method for expanding the luminance Range of the maximum luminance value. Specifically, the conventional method of the luminance Range corresponding to the TV signal is called SDR (Standard Dynamic Range), the maximum luminance value is 100nit, and the HDR assumes that the maximum luminance value is increased to 1000nit or more. As HDR, SMPTE (Society of Motion Picture and Television Engineers, USA) and ITU-R (International Telecommunications Union Radio Communications Sector, International telecommunication Union Wireless Communications Commission) are being standardized.

As a specific application target of HDR, it is assumed that it is used in broadcasting, a box medium (Blu-ray (registered trademark, the same as below), etc.), internet distribution, and the like, as in HD and UHD.

In the following description, in a video corresponding to HDR, the luminance of the video is constituted by luminance values in a luminance range of HDR, and a luminance signal obtained by quantizing the luminance values of the video is referred to as an HDR signal. In the video corresponding to the SDR, the luminance of the video is constituted by the luminance values in the luminance range of the SDR, and a luminance signal obtained by quantizing the luminance values of the video is referred to as an SDR signal.

[1-2. relationship between master generation and distribution method and display device ]

Fig. 2 is a diagram for explaining the relationship between the video creation and distribution method and the display device when a new video presentation is introduced to content.

When a new image expression (an increase in the number of pixels, etc.) is introduced for the purpose of image quality improvement, as shown in fig. 2, (1) it is necessary to change a master suitable for a home entertainment system on the image creation side. In response to this, (2) the distribution system of broadcast, communication, cassette media, and the like also needs to be updated, and (3) the display device such as a TV, a projector, and the like that displays the video also needs to be updated.

[1-3. relationship between master, distribution method, and display device when HDR is introduced ]

In order for a user to enjoy content (e.g., high-luminance video content (HDR content)) corresponding to a new video presentation at home, it is necessary to newly introduce both an HDR-compliant distribution method and an HDR-compliant display device. That is, in order to enjoy content corresponding to a new video presentation at home, the user needs to prepare a distribution method and a display device corresponding to the new video presentation. These are inevitable when new video representations are introduced, such as when the video from SD is changed to HD, when the video from HD is changed to 3D, and when the video from HD is changed to UHD (4K).

Therefore, there is a need to exchange TVs that are expensive and not easily replaceable in terms of size, weight, and the like. The change to a new video presentation depends on the spread of display devices (e.g., TV) having new functions. Since large investment cannot be made in media content at first, the popularization of new video presentation is delayed.

Therefore, as shown in fig. 3, in order to fully embody the original HDR image even for the HDR, it is predicted that a TV (hereinafter referred to as "HDRTV") suitable for displaying an image corresponding to the HDR (hereinafter referred to as "HDR display") needs to be purchased.

[1-4.SDRTV]

A TV (hereinafter referred to as "SDRTV") which is applied only to display of a video corresponding to SDR (hereinafter referred to as "SDR display") is generally input with an input signal having a luminance value of 100 nit. Therefore, the SDRTV is sufficient to express the luminance value of the input signal as long as its display capability is 100 nit. However, SDRTV has a function of reproducing an image with an optimal luminance value according to viewing environments (dark room: theater mode, bright room: dynamic mode, etc.), and there are many SDRTVs having a capability of reproducing an image representation of 200nit or more. That is, such an SDRTV can display a video with a maximum luminance (for example, 300nit) up to the display capability by selecting a display mode corresponding to the viewing environment.

However, since the upper limit of the luminance of the input signal is determined to be 100nit in the input signal of the SDR method to which the SDRTV is input, it is difficult to use the high-luminance video reproduction capability of more than 100nit which the SDRTV has for the reproduction of the HDR signal, as long as the input interface of the SDR method is used as in the related art (see fig. 4A and 4B).

[1-5.HDR → SDR transform ]

High-brightness video content (hereinafter also referred to as "HDR content" or "HDR video") is assumed to be output from SDRTV by a playback device (e.g., Set Top Box (STB), Blu-ray equipment, or IPTV playback equipment) adapted to HDR, and distributed by a distribution method such as broadcast adapted to HDR, video distribution via a communication network, or a package medium (e.g., Blu-ray Disc adapted to HDR) adapted to HDR. When HDR content is reproduced in an SDRTV, [ HDR → SDR transformation ] is implemented to transform an HDR signal corresponding to HDR into an SDR signal having an SDR luminance range with a maximum value of 100nit, so that a video can be correctly displayed in the SDRTV. Thus, the SDRTV can display an SDR video converted from an HDR video using the converted SDR signal (see fig. 5).

However, in this case, even though the user purchases the content to which HDR is applied (for example, Blu-ray disc, HDR, and IPTV content) and the playback device to which HDR is applied (for example, Blu-ray device, and IPTV playback device to which HDR is applied), the user can enjoy the video only by the video representation of SDR (SDR representation) in SDRTV. That is, even if HDR content and a playback device applied to HDR are prepared, if there is no display device (e.g., HDRTV) applied to HDR but only SDRTV, video cannot be viewed by video representation (HDR representation) of HDR.

Therefore, if the user cannot prepare the HDRTV, the user cannot know the value of the HDR even if the HDR content and the transmission medium (reproduction apparatus) are purchased (i.e., the HDR is high quality and is superior to the SDR). Thus, since the user cannot understand the value of HDR without HDRTV, it can be said that the popularization of HDR content and an applicable distribution method of HDR is determined by the speed of popularization of HDRTV.

[1-6. two ways of implementing HDR → SDR transformations ]

In the case of transmitting an HDR signal to a TV using a Blu-ray disc (BD), two cases are assumed as shown in fig. 6A and 6B described below. Fig. 6A is a diagram for explaining a case where only an HDR signal corresponding to HDR is stored in a BD to which HDR is applied. Fig. 6B is a diagram for explaining a case two in which an HDR signal corresponding to HDR and an SDR signal corresponding to SDR are stored in a BD to which HDR is applied.

As shown in fig. 6A, in the first case, when displaying a video obtained by reproducing a BD by a Blu-ray device, the Blu-ray device does not need to convert a luminance signal stored in the BD and outputs the luminance signal to the HDRTV directly, regardless of whether the BD suitable for HDR (hereinafter, referred to as "HDRBD") or the BD suitable for SDR (hereinafter, referred to as "SDRBD") is reproduced. Further, since the HDRTV performs display processing on both the HDR signal and the SDR signal, the HDRTV performs display processing corresponding to the input luminance signal and displays an HDR video or an SDR video.

On the other hand, in the first case, when displaying a video obtained by reproducing a BD by a Blu-ray device in an SDRTV, the Blu-ray device performs conversion processing for converting an HDR signal into an SDR signal when reproducing an HDRBD, and outputs the SDR signal obtained by the conversion processing to the SDRTV. Also, when reproducing the SDRBD, the Blu-ray device directly outputs to the SDRTV without converting the SDR signal stored in the BD. Thus, the SDRTV displays the SDR image.

In the case two, as shown in fig. 6B, when displaying a video obtained by reproducing the BD by the Blu-ray apparatus, the HDRTV is the same as the case one.

On the other hand, in the second case, when the SDRTV is caused to display a video obtained by the BD playback by the Blu-ray apparatus, the Blu-ray apparatus does not need to convert the SDR signal stored in the BD, and outputs the SDR signal to the SDRTV directly, both when the HDRBD is played back and when the SDRBD is played back.

In both cases one and two, even if the Blu-ray equipment for which HDRBD and HDR are applicable is purchased, only SDR video can be enjoyed without HDRTV. Therefore, the user needs HDRTV to view HDR video, and it is predicted that the popularization of the HDR-compliant Blu-ray equipment or HDRBD requires time.

[1-7.HDR → approximate HDR transform ]

From the above, it is important to be able to advance development of HDR content and distribution systems without waiting for popularization of HDRTV in order to promote popularization of HDR. Therefore, if the HDR signal can be viewed as not an SDR video but an HDR video or an HDR-like video closer to the HDR video than the SDR video in the existing SDRTV, a user can view a video having a higher image quality close to the HDR video, which is significantly different from the SDR video, without purchasing the HDRTV. That is, if the user can view the near-HDR video in the SDRTV, the user can view a video having higher quality than the SDR video by preparing only the HDR content and the HDR distribution device without preparing the HDRTV. In short, enabling the viewing of near HDR video in SDRTV would likely be an incentive for users to purchase HDR content and HDR distribution equipment (see fig. 7).

In order to display an approximate HDR image in SDRTV, the following [ HDR → approximate HDR transformation processing ] needs to be implemented: in a configuration in which an SDRTV is connected in an HDR distribution system, when reproducing HDR content, instead of converting an HDR signal into an SDR video signal, an approximate HDR signal for displaying a video having a maximum luminance of, for example, 200nit or more of the display capability of the SDRTV is generated using an input of a video signal having 100nit of the SDRTV as a maximum value, and the generated approximate HDR signal is transmitted to the SDRTV, so that a video of the HDR content can be accurately displayed in the SDRTV.

[1-8. about EOTF ]

Here, the EOTF will be described with reference to fig. 8A and 8B.

Fig. 8A is a diagram showing an example of an EOTF (Electro-Optical Transfer Function) corresponding to HDR and SDR.

The EOTF is generally called a gamma curve, and represents a correspondence relationship between code values and luminance values for converting the code values into luminance values. That is, the EOTF is relationship information indicating a correspondence relationship between a plurality of code values and luminance values.

Fig. 8B is a diagram showing an example of the inverse EOTF corresponding to each of the HDR and SDR.

The inverse EOTF represents a correspondence relationship between a luminance value and a code value, and is information for converting the luminance value into a code value by quantizing it, contrary to the EOTF. That is, the inverse EOTF is relationship information indicating a correspondence relationship between a luminance value and a plurality of code values. For example, when a luminance value of a video corresponding to HDR is expressed by a code value of 10-bit gradation, luminance values in a luminance range up to HDR of 10,000nit are quantized and mapped to 1024 integer values of 0 to 1023. That is, by performing quantization in accordance with the inverse EOTF, luminance values in a luminance range up to 10,000nit (luminance values of a video corresponding to HDR) are converted into an HDR signal of a code value of 10 bits. In the EOTF corresponding to HDR (hereinafter referred to as "EOTF for HDR") or the inverse EOTF corresponding to HDR (hereinafter referred to as "inverse EOTF for HDR"), a luminance value higher than that of the EOTF corresponding to SDR (hereinafter referred to as "EOTF for SDR") or that of the inverse EOTF corresponding to SDR (hereinafter referred to as "inverse EOTF for SDR") can be expressed, and for example, in fig. 8(a) and 8(B), the maximum value (peak luminance) of the luminance is 10,000 nit. That is, the luminance range of HDR includes the entire luminance range of SDR, and the peak luminance of HDR is larger than the peak luminance of SDR. The luminance range of HDR is a luminance range that extends the maximum value from 100nit, which is the maximum value of the luminance range of SDR, to 10,000 nit.

For example, regarding the EOTF of HDR and the reverse EOTF of HDR, SMPTE 2084 standardized by the american Society of Motion Picture and Television Engineers (SMPTE) may be mentioned as an example.

[1-9. method of Using EOTF ]

Fig. 9 is an explanatory diagram of a method of determining a code value of a luminance signal stored in a content, and a flow of restoring a luminance value from the code value at the time of reproduction.

The luminance signal representing luminance in this example is an HDR signal corresponding to HDR. The ranked image is quantized by the inverse EOTF of HDR, and a code value corresponding to a luminance value of the image is determined. Image coding or the like is performed based on the code value, and a stream of video is generated. At the time of reproduction, the stream decoding result is inversely quantized according to the HDR EOTF, and is thereby converted into a linear signal, and the luminance value of each pixel is restored. Hereinafter, quantization of an inverse EOTF using HDR will be referred to as "EOTF transform of inverse HDR". The inverse quantization of the EOTF using HDR is referred to as "HDR EOTF transform". Similarly, quantization using the inverse EOTF of the SDR is referred to as "inverse SDR EOTF transform". The inverse quantization of the EOTF using the SDR is referred to as "SDR EOTF transform".

[1-10. necessity of approximating HDR ]

Next, the necessity of approximating HDR will be described with reference to fig. 10A to 10C.

Fig. 10A is a diagram showing an example of display processing for converting an HDR signal in an HDRTV and displaying the HDR signal.

As shown in fig. 10A, in the case of displaying an HDR image, the maximum value (Peak luminance (hpl) (HDR Peak luminance): for example, 1500nit)) of the luminance range of the HDR may not be directly displayed even if the display device is an HDRTV. In this case, luminance conversion is performed so that a linear signal obtained by performing inverse quantization of the EOTF using HDR matches a maximum value (dpl (display Peak luminance): for example, 750nit) of a luminance range of the display device. Then, by inputting the video signal obtained by performing luminance conversion to the display device, it is possible to display an HDR video that matches the luminance range of the maximum value that is the threshold of the display device.

Fig. 10B is a diagram showing an example of display processing for HDR display using a playback device to which HDR is applied and an SDRTV.

As shown in fig. 10B, in the case where an HDR video is displayed, if the display device is an SDRTV, and if the maximum value (peak luminance (DPL: 300nit, for example)) of the luminance range of the SDRTV to be displayed exceeds 100nit, in the "HDR → approximate HDR conversion processing" in the playback device (Blu-ray apparatus) to which HDR is applied in fig. 10B, "EOTF conversion for HDR performed in the HDRTV" and "luminance conversion" using DPL (300 nit, for example) that is the maximum value of the luminance range of the SDRTV are performed, if a signal obtained by performing the "luminance conversion" is directly input to the "display device" of the SDRTV, the same effect as that of the HDRTV can be achieved even when the SDRTV is used.

However, in the SDRTV, there is no unit for directly inputting such a signal from the outside, and thus it cannot be realized.

Fig. 10C is a diagram showing an example of display processing for HDR display using a playback device and an SDRTV that are connected to each other via a standard interface and are suitable for HDR.

As shown in fig. 10C, it is generally necessary to input a signal such as that which can obtain the effect of fig. 10B to the SDRTV using an input interface (HDMI (registered trademark) or the like) provided to the SDRTV. In the SDRTV, a signal input through an input interface sequentially passes through "EOTF conversion by SDR", "luminance conversion for each mode", and "display device", and a video image in accordance with a luminance range of a maximum value of the display device is displayed. Thus, signals (approximate HDR signals) such as "EOTF transform of SDR" and "luminance transform per mode" that can cancel the pass immediately after the input interface in SDRTV are generated in the HDR compliant Blu-ray device. That is, in the Blu-ray apparatus to which HDR is applied, the same effect as that when a signal immediately after "luminance conversion" is input to the "display device" (dotted arrow in fig. 10C) is approximately achieved by performing "inverse luminance conversion for each mode" and "inverse SDR EOTF conversion" immediately after "EOTF conversion for HDR" and "luminance conversion" using peak luminance (DPL) of SDRTV.

[1-11. inverter and display device ]

Fig. 11 is a block diagram showing the configuration of the converter and the display device according to the embodiment. Fig. 12 is a flowchart showing a conversion method and a display method performed by the conversion device and the display device according to the embodiment.

Hereinafter, the luminance range (0 to HPL [ nit ]) of HDR is referred to as "1 st luminance range". The luminance range (0 to DPL [ nit ]) of the display is denoted as "2 nd luminance range". The luminance range (0 to 100[ nit ]) of the SDR is expressed as a "3 rd luminance range".

[1-12. conversion method and display method ]

More specifically, in the conversion from the SDR signal (approximate HDR signal) to the display luminance value, in step S106, the code value of the SDR associated with the code value of the SDR in the obtained SDR signal is determined using the EOTF in which the luminance value in the luminance range of the SDR and the plurality of 3 rd code values are associated with each other.

In the conversion into the display luminance value, in step S107, a display luminance value corresponding to the luminance range of the display, which is previously associated with the determined SDR luminance value, is determined, and the 3 rd luminance conversion of converting the SDR luminance value corresponding to the SDR luminance range into the display luminance value corresponding to the luminance range of the display is performed.

[1-13. 1 st luminance conversion ]

Next, the details of the 1 st luminance conversion (HPL → DPL) in step S102 will be described with reference to fig. 13A. Fig. 13A is a diagram for explaining an example of the 1 st luminance conversion.

In the 1 st luminance conversion, CAL and CPL in the content luminance information are used, and the luminance value below or near CAL is the same before and after the conversion, and only the luminance value above or near CPL is changed. That is, as shown in fig. 13A, in the 1 st luminance conversion, when the luminance value of the HDR is CAL or less, the luminance value of the HDR is determined as the display luminance value without being converted, and when the luminance value of the HDR is CPL or more, the DPL that is the 2 nd maximum luminance value is determined as the display luminance value.

In the 1 st luminance conversion, the peak luminance (CPL) of the HDR image in the luminance information is used, and when the luminance value of the HDR is CPL, the DPL is determined as the display luminance value.

[1-14. 2 nd luminance conversion ]

Next, the details of the 2 nd luminance conversion (DPL → 100[ nit ]) in step S103 will be described with reference to fig. 14. Fig. 14 is a diagram for explaining the 2 nd luminance conversion.

Through the above-described processing, the 2 nd luminance conversion converts the display luminance value (input luminance value) of the 2 nd luminance range, that is, the luminance range of the display, into the luminance value (output luminance value) of the SDR of the 3 rd luminance range, that is, the luminance range of the SDR.

In the 2 nd luminance conversion, the conversion formula is switched according to the display mode of the SDR display. For example, when the display mode of the SDR display is a normal mode, the luminance is converted into a proportional value proportional to the display luminance value. In the 2 nd luminance conversion, when the display mode of the SDR display is a dynamic mode in which the high-luminance pixel is brighter than the normal mode and the low-luminance pixel is darker, the inverse function thereof is used to convert the luminance value of the SDR of the low-luminance pixel into a luminance value higher than a proportional value proportional to the luminance value of the display and convert the luminance value of the SDR of the high-luminance pixel into a luminance value lower than a proportional value proportional to the luminance value of the display. That is, in the 2 nd luminance conversion, the luminance value associated with the display luminance value determined in step S102 is determined as the luminance value of the SDR using the luminance-related information corresponding to the display characteristic information which is the information indicating the display characteristic of the SDR display, and the luminance conversion processing is switched according to the display characteristic information. The luminance-related information corresponding to the display characteristic information is, for example, information obtained by associating a display luminance value (input luminance value) set for each display parameter (display mode) of the SDR display with a luminance value (output luminance value) of the SDR, as shown in fig. 14.

[1-15. display settings ]

Next, the details of the display setting in step S105 will be described with reference to fig. 15. Fig. 15 is a flowchart showing a specific process of the display setting.

In the setting of the display setting (S105) according to steps S201 to S203, the EOTF set in the SDR display is set as the recommended EOTF corresponding to the acquired setting information. By setting in this manner, in step S106 performed subsequent to step S105, the luminance value of the SDR can be determined using the recommended EOTF.

Then, the approximate HDR video (SDR signal) is displayed on the SDR display, but it is determined whether or not the display parameters of the SDR display match the setting information using the setting information before the display (S205).

In the setting of the display setting (S105) according to steps S204 to S207, the display parameter set to the SDR display is set as the recommended display parameter corresponding to the acquired setting information.

If it is determined that the switching cannot be performed on the system side (S206: NO), a message urging the user to change the display parameters set in the SDR display by manual operation is displayed on the screen (S208). For example, a message "please set the display mode to the dynamic mode and set the backlight to the maximum" is displayed on the screen. That is, when the display parameters set to the SDR display cannot be switched in the setting (S105), a message urging the user to switch the display parameters set to the SDR display to the recommended display parameters is displayed on the SDR display.

[1-16. 3 rd luminance conversion ]

Next, the details of the 3 rd luminance conversion (100 → DPL [ nit ]) in step S107 will be described with reference to fig. 16. Fig. 16 is a diagram for explaining the 3 rd luminance conversion.

In the 3 rd luminance conversion, the conversion formula is switched according to the display mode of the SDR display. For example, when the display mode of the SDR display is the normal mode (that is, when the set display parameter is a parameter corresponding to the normal mode), the display luminance value luminance is converted into a proportional value proportional to the luminance value of the SDR. In the 3 rd luminance conversion, when the display mode of the SDR display is a dynamic mode in which the high-luminance pixel is brighter than the normal mode and the low-luminance pixel is darker, the display luminance value of the low-luminance pixel is converted into a luminance value lower than a proportional value proportional to the luminance value of the SDR, and the display luminance value of the high-luminance pixel is converted into a luminance value higher than a proportional value proportional to the luminance value of the SDR. That is, in the 3 rd luminance conversion, the luminance value of the SDR determined in step S106 is determined as a display luminance value in advance by using luminance-related information corresponding to a display parameter indicating the display setting of the SDR display, and the luminance conversion processing is switched according to the display parameter. The luminance-related information corresponding to the display parameters is, for example, information obtained by associating a luminance value (input luminance value) of SDR set for each display parameter (display mode) of the SDR display with a display luminance value (output luminance value), as shown in fig. 16.

[1-17. Effect, etc. ]

Although the input signal of a typical SDRTV is 100nit, it has a capability of realizing video representation of 200nit or more in accordance with the viewing environment (darkroom: cinema mode, bright room: dynamic mode, etc.). However, the upper limit of the luminance of the input signal for the SDRTV is set to 100nit, and thus this capability cannot be directly utilized.

When displaying an HDR video in an SDRTV, the HDR video is not converted into an SDR video having a luminance value of 100nit or less but is subjected to an "HDR → approximate HDR conversion process" so as to maintain a gradation in a luminance range exceeding 100nit to some extent, by utilizing the characteristic that the peak luminance of the SDRTV to be displayed exceeds 100nit (usually 200nit or more). Therefore, it is possible to display an approximate HDR video close to the original HDR in the SDRTV.

In the case where this "HDR → approximate HDR conversion processing" technique is applied to the Blu-ray, as shown in fig. 17, only the HDR signal is stored in the HDR disc, and in the case where the Blu-ray device is connected to the SDRTV, the Blu-ray device performs the "HDR → approximate HDR conversion processing" to convert the HDR signal into an approximate HDR signal and transmits the approximate HDR signal to the SDRTV. Thus, the SDRTV can display a video having an approximate HDR effect by converting the received approximate HDR signal into a luminance value. Thus, when there is no HDR-compliant TV, it is possible to display an approximate HDR video having a higher quality than an SDR video even in the case of an SDRTV, by preparing a BD to which HDR is compliant and a Blu-ray device to which HDR is compliant.

Therefore, although it is considered that HDR-compliant TV is required for viewing HDR video, it is possible to view, in an existing SDRTV, approximate HDR video that can actually feel the effect of HDR.

HDR signals transmitted by broadcast, a box medium such as Blu-ray, or the like, or internet distribution such as OTT are subjected to HDR → approximate HDR conversion processing, and thereby converted into approximate HDR signals. Therefore, the HDR signal can be displayed as an approximate HDR signal in the existing SDRTV.

[ other embodiments ]

As described above, the embodiments have been described as an example of the technique disclosed in the present application. However, the technique in the present application is not limited to this, and can be applied to an embodiment in which appropriate changes, substitutions, additions, omissions, and the like are made. Further, the components described in the above embodiments may be combined to form a new embodiment.

Therefore, other embodiments are exemplified below.

The HDR video is, for example, video in a blu-ray disc, a DVD, a moving picture distribution site of the internet, a broadcast, or an HDD.

The display device 200(SDR display unit) is, for example, a television, a personal computer, or a smartphone.

The CPL or CAL of the HDR image may be present for one content or may be present for each scene. That is, in the conversion method, luminance information (CPL, CAL) including at least one of a 1 st maximum luminance value, which is a maximum value among luminance values corresponding to a plurality of images constituting the scene, and an average luminance value, which is an average of luminance values corresponding to the plurality of images constituting the scene, may be acquired for each of the scenes as luminance information corresponding to each of the plurality of scenes of the video, and in the 1 st luminance conversion, a display luminance value may be determined for each of the plurality of scenes based on the luminance information corresponding to the scene.

Also, the HDR EOTF may not be SMPTE 2084, and other kinds of HDR EOTF may be used. The maximum luminance (HPL) of the HDR image may be not 10,000nit, and may be 4,000 nit or 1,000 nit, for example.

Also, the bit width of the code value may be, for example, 16, 14, 12, 10, 8 bits.

The display mode may be a fixed mode or may not be included in the display characteristic information.

[ mathematical formula 1 ]

Here, L represents a luminance value normalized to 0 to 1, and S1, S2, a, b, and M are values set based on CAL, CPL, and DPL. ln is the natural logarithm. V is a luminance value normalized to 0-1 after conversion. As shown in the example of fig. 8A, when CAL is 300nit, CPL is 2,000 nit, DPL is 750nit, and conversion is performed to CAL +50nit or more without conversion, the respective values are, for example, the following values.

S1＝350/10000

S2＝2000/10000

M＝750/10000

a＝0.023

b＝S1-a*ln(S1)＝0.112105

That is, in the 1 st luminance transformation, when the luminance value of the SDR is between the average luminance value (CAL) and the 1 st maximum luminance value (CPL), the display luminance value corresponding to the luminance value of the HDR is determined using the natural logarithm.

By converting an HDR image using information such as content peak luminance or content average luminance of the HDR image, the conversion formula is changed according to the content, and the HDR image is converted so as to maintain the gradation as much as possible. Further, adverse effects of over-darkness and over-brightness can be suppressed. Specifically, the content peak luminance of the HDR image is mapped to the display peak luminance, thereby maintaining the gradation as much as possible. Further, by not changing the pixel value near or below the average luminance, the overall brightness does not change.

The HDR image is converted using the peak luminance value and the display mode of the SDR display, the conversion formula can be changed according to the display environment of the SDR display, and an image having a feeling of HDR (an image close to HDR) can be displayed with the same gradation or brightness as the original HDR image in accordance with the performance of the SDR display. Specifically, the peak luminance of the display is determined by the maximum luminance and the display mode of the SDR display, and the HDR image is converted so as not to exceed the peak luminance value, and the HDR image is displayed without reducing the gradation of the HDR image until the luminance that can be displayed by the SDR display, whereby the luminance that cannot be displayed is reduced by the luminance value until the luminance that can be displayed.

As described above, the brightness information that cannot be displayed is reduced, and the display can be performed in a form close to the original HDR image without reducing the gradation of the brightness that can be displayed. For example, in the case of a display having a peak luminance of 1,000 nit, the luminance value is changed according to the display mode of the display while maintaining the overall brightness by converting the image into an approximate HDR image controlled to have a peak luminance of 1,000 nit. Therefore, the conversion formula of the luminance is changed according to the display mode of the display. If a luminance larger than the peak luminance of the display is allowed in the near HDR image, the large luminance may be replaced with the peak luminance on the display side to be displayed, and in this case, the entire image may be darker than the original HDR image. Conversely, when luminance smaller than the peak luminance of the display is converted into the maximum luminance, the small luminance is replaced with the peak luminance on the display side, and the entire HDR image becomes brighter than the original HDR image. Further, since the peak luminance is smaller than the peak luminance on the display side, the performance related to the gradation of the display cannot be used to the maximum.

Further, on the display side, by switching the display setting using the setting information, it is possible to display the approximate HDR image more favorably. For example, when the brightness is set to be dark, the HDR feeling is impaired because high-brightness display cannot be performed. In this case, by changing the display setting or displaying a message prompting the change, the performance of the display can be exhibited to the maximum extent, and a high-gradation image can be displayed.

In the content of Blu-ray, etc., a video signal and a graphic signal such as a subtitle and a menu are multiplexed as independent data. When reproducing, they are decoded individually, and the decoding results are synthesized and displayed. Specifically, the plane of subtitles and menus is superimposed on the plane of the video.

Among them, even when the video signal is HDR, a graphic signal such as subtitles and menus may become SDR. In the HPL → DPL conversion of a video signal, the following two types of conversion (a) and (b) can be performed.

(a) Case where HPL → DPL transform is implemented after graphics synthesis

1. The EOTF of the graph is transformed from the EOTF of the SDR to the EOTF of the HDR.

2. And synthesizing the graphics subjected to the EOTF conversion with the video.

3. The synthesis result is subjected to HPL → DPL transform.

(b) Case where HPL → DPL transform is performed before graphics synthesis

1. The EOTF of the graph is transformed from the EOTF of the SDR to the EOTF of the HDR.

2. The video is subjected to the HPL → DPL transform.

3. And synthesizing the graph after the EOTF conversion and the video after the DPL conversion.

In addition, the order of 1 and 2 in case (b) may be changed.

In both the modes (a) and (b), the peak luminance of the graphics is 100nit, but when the DPL is high luminance such as 1000nit, for example, the luminance of the graphics may decrease with respect to the video after the HPL → DPL conversion while the luminance of the graphics remains 100 nit. In particular, it is conceivable that subtitles superimposed on a video are darkened. Therefore, for graphics, luminance may also be converted in accordance with the value of DPL. For example, the brightness of the subtitles may be converted according to a set value, such as a value set to be a percentage of the DPL value. Graphics other than subtitles such as menus can be processed in the same manner.

The above description has been made on the reproduction operation of the HDR disc in which only the HDR signal is stored.

Next, the multiplexed data stored in the dual disc in which both the HDR signal and the SDR signal are stored, which is shown in the second case of fig. 6B, will be described with reference to fig. 18. Fig. 18 is a diagram for explaining multiplexed data stored in a Dual Disc (Dual Disc).

In the dual disc, as shown in fig. 18, the HDR signal and the SDR signal are stored as multiplexed streams different from each other. For example, in an optical disc such as Blu-ray, data of various media such as video and audio, subtitles, graphics, etc. is stored as one multiplexed stream in accordance with an MPEG-2 TS-based multiplexing scheme called M2 TS. These multiplexed streams are referred to by metadata for reproduction control such as a playlist, and when reproduced, the player analyzes the metadata to select a multiplexed stream to be reproduced or data in an independent language stored in the multiplexed stream. In this example, the case where play lists for HDR and SDR are stored independently and each play list refers to an HDR signal or an SDR signal is shown. In addition, identification information indicating that both the HDR signal and the SDR signal are stored may be separately shown.

Although both HDR and SDR signals can be multiplexed in the same multiplexed stream, it is necessary to perform multiplexing so as to satisfy a buffer model such as T-std (system Target decoder) defined in MPEG-2TS, and it is particularly difficult to multiplex two pieces of video with high bit rates within a range of a preset data read rate. Therefore, it is desirable to separate the multiplexed streams.

Data such as audio, subtitle, or graphics needs to be stored for each multiplexed stream, and the amount of data increases compared to when multiplexed in one stream. However, with respect to an increase in the amount of data, the amount of data of a video can be reduced using a video encoding method with a high compression rate. For example, by changing MPEG-4AVC used in conventional Blu-ray to HEVC (high Efficiency Video coding), it is expected that the compression rate will be improved by 1.6 to 2 times. Further, the combination of HDR and SDR of 2K and the combination of SDR of 4K and HDR of 2K, that is, the combination of two 2K or the combination of 2K and 4K, etc. may be stored in the dual disc, and the storage of two 4K is prohibited, so that only the combination controlled within the capacity of the optical disc is permitted.

Fig. 19 is a flowchart showing the playback operation of the dual disc.

First, the playback device determines whether or not the optical disc to be played back is a dual disc (S301). When it is determined that the TV is a dual disk (S301: YES), it is determined whether the TV to be outputted is HDRTV or SDRTV (S302). If it is determined to be HDRTV (S302: YES), the process proceeds to step S303, and if it is determined to be SDRTV (S302: NO), the process proceeds to step S304. In step S303, an HDR video signal is acquired from a multiplexed stream including HDR signals in the dual disc, decoded, and output to the HDRTV. In step S304, an SDR video signal is acquired from a multiplexed stream including SDR signals in the dual disc, decoded, and output to the SDRTV. When it is determined in step S301 that the playback target is not a dual disc (S301: no), the playback permission is determined according to a predetermined method, and the playback method is determined according to the determination result (S305).

In the conversion method of the present invention, when displaying an HDR video in an SDRTV, by using a case where the peak luminance of the SDRTV to be displayed exceeds 100nit (usually 200nit or more), instead of converting the HDR video into an SDR video of 100nit or less, the conversion method performs "HDR → approximate HDR conversion processing" that can convert the HDR video into an approximate HDR video close to the original HDR and display the image in the SDRTV while maintaining the gradation of a region exceeding 100nit to some extent.

In the conversion method, the conversion method of "HDR → approximate HDR conversion processing" may be switched according to the display characteristics (maximum luminance, input/output characteristics, and display mode) of the SDRTV.

As the acquisition method of the display characteristic information, there may be considered (1) automatic acquisition through HDMI and a network, (2) generation by letting a user input information such as a manufacturer name, a model number, and the like, and (3) acquisition from a cloud or the like using the information such as the manufacturer name, the model number, and the like.

In the conversion method, the conversion method may be switched according to luminance information (CAL, CPL) of the HDR video.

As details of the conversion method, (1) conversion is performed so as not to exceed the DPL, (2) conversion is performed so as to make the CPL reach the DPL, (3) the CAL and the luminances around the CAL are not changed, (4) conversion is performed using a natural logarithm, and (5) clipping processing is performed in the DPL.

In the above embodiments, each component may be configured by dedicated hardware, or may be realized by executing a software program corresponding to each component. Each component can be realized by reading out a software program recorded in a storage medium such as a hard disk or a semiconductor memory by a program execution unit such as a CPU or a processor.

The display method and the display device according to one or more embodiments of the present application have been described above based on the embodiments, but the present application is not limited to the embodiments. Various modifications that can be made to the present embodiment by those skilled in the art may be made without departing from the spirit of the present application, and a configuration in which the components in different embodiments are combined is also included in one or more ranges of the present application.

Industrial applicability

The present invention is applied to a conversion method, a conversion device, and the like capable of appropriately converting luminance from a 1 st luminance range to a 2 nd luminance range in which the luminance range is reduced.

Description of the reference symbols

100 a conversion device; 101 a conversion unit; 102 a luminance conversion unit; 103 an inverse luminance converting section; 104 EOTF conversion part for inverse SDR; 200 a display device; 201 a display setting unit; 202 SDR; 203 a luminance conversion unit; 204 display unit.